Primarily aimed at smartphone users, the "bumpers" will run in front of videos and last for six seconds each.

Product Manager Zach Lupei has called them "little haikus of video ads" and they will force advertisers to get creative within the short time frame.

Rolling out this month, advertisers will initially be testing the difference in impact between the unskippable bumpers and the traditional TrueView ads (which can last any length but can be skipped almost immediately).

YouTube has said that early tests show the bumpers brought an improvement in recall, awareness and consideration. It also said they are most effective when paired with TrueView and Google Preferred ads.

If you have a Google Play Music/YouTube Red subscription, you can opt out of the ads altogether.